If you're just getting comfortable with Facebook and Twitter, you might want to brace yourself: Foursquare, the hottest among a rising new class of social networks, is gaining ground.
Dubbed the "next Twitter" by some tech experts, Foursquare.com doesn't just let you stay in touch with your friends; it adds a "check-in" feature that lets your friends tell you where they are, and it lets you compete with them for virtual badges and titles as you visit favorite haunts.
As users check in at participating restaurants or bars, for instance, they can leave tips for their friends -- "try the tuna salad!" -- and earn virtual points. The user who visits a site the most gets dubbed its "mayor," an honor businesses sometimes reward with special deals.
As odd as it might seem to the uninitiated, Foursquare fans seem to find the gaming component almost addictive.
"I just became the mayor of PetSmart on @Foursquare!" a guy from Huntersville, N.C., recently boasted on the network.
Wrote a Charlotte, N.C., woman: "I can't believe I got ousted as mayor of my own studio."
The idea of location-aware social networking isn't new. Twitter can show users' locations, though the feature can be turned off. And some location-based networks have been around for years. But with smart phones increasingly sophisticated and popular, fast-growing networks such as Foursquare and rival upstart Gowalla are poised to take the concept to the next level.
Their progress isn't without peril: Privacy experts warn that broadcasting your location might not be a good idea, especially for teens.
That hasn't stopped new users from hopping aboard Foursquare, the New York-based start-up founded by Dennis Crowley, a tech entrepreneur who sold a similar network to Google in 2005.
Only about a year old, Foursquare has distinguished itself in recent months by snagging hundreds of thousands of new users and heavy media buzz. Businesses ranging from the Bravo television network to local eateries have been signing partnership deals, hoping to reward repeat customers and lure their smart-phone-carrying friends with real-time discounts and recommendations.
Foursquare became available in Charlotte around October. While the company says temporary software problems prevent it from tallying its Charlotte users, fans here estimate their number in the hundreds.
Late last year, for instance, UNC Charlotte registered its dining halls and coffee shops -- the first university in the nation, it says, to use Foursquare to push dining services information and promotions to students and faculty.
Crown Commons, a dining hall in the Student Union, had 63 check-ins at one point last week, and several students recommended the pizza to their friends.
"It's a fairly new thing," said York Brady, a freshman at UNC Charlotte. "The only ones who seem to know about it are the ones who are really into technology."
Brian Baute, a UNC Charlotte Internet technology director, said that's changing: "It's getting to where more and more of our students on campus know about it and have access to it. We're expecting it to grow over time."
If national statistics are any guide, he won't be disappointed. Foursquare says it had about 250,000 users nationally just before New Year's Day, but its growth has accelerated so rapidly that it expects to top half a million in the next two weeks.
That's still tiny when compared with Facebook's 400 million-plus users. But with revenues for mobile location-based networks projected to top $12 billion by 2014, Internet giants like Facebook and Google are paying attention.
Google included mobile check-ins with its recently launched Buzz social network, and the business blog Silicon Valley Insider recently reported that Facebook is developing its own location-aware check-in feature.
"It's definitely a hot area," said Allison Mooney, an official with MobileBehavior, a consulting firm that studies how consumers use wireless technology. "There is a certain amount of social capital and bragging rights that come with being the 'mayor' of a popular bar or the person that goes out the most in New York City."
Still, critics worry about potential privacy dangers.
Google retooled Buzz after users objected to the fact that it publicly displayed their most frequent e-mail contacts. An Internet privacy think tank filed a federal complaint, accusing Google of turning people's private Gmail data into public social networking information.
Local Twitter users in recent weeks have been sending each other warnings about Please Rob Me, a Web site that aggregates Twitter and Foursquare status updates to show when homeowners aren't home.
The people behind the site, pleaserobme.com, say they were making a point about the privacy concerns inherent in broadcasting users' real-time location.
Point taken, some locals say.
"I'm being a lot more cautious as to who I let become my friends" on Foursquare, said Brandon Uttley, a social media strategist with more than 6,000 Twitter followers. "It becomes too easy for people to use it against us."
Charlotte Foursquare users say they are being careful, but they aren't dropping the service.
Chad Huck, a 29-year-old nursing student, had logged 379 check-ins around town as of last week, with so many of them coming from spots around UNCC that he'd become the university's Foursquare "mayor."
"I'm a very social person," Huck said. "I like the fact that I can see where my friends are."
Asked about the possibility of criminals using it to rob his home, he replied, "My German shepherd would take care of them."
Explore further: A Closer Look: Your (online) life after death